1. Field of the Invention
The present invention relates to a semiconductor device (hereinafter sometimes referred to as an xe2x80x9cICxe2x80x9d), a mounting structure thereof, a liquid crystal device using the mounting structure, and an electronic apparatus using the liquid crystal device.
2. Description of the Related Art
With either the COG (chip on glass) or COF (chip on film) mounting methods, mounting a face-down-bonding type IC using an ACF (anisotropic conductive film) makes it possible to cope with fine pitches and to collectively connect a plurality of contacts electrically, thus making the method suitable for mounting a driving IC on electrode terminals formed on a liquid crystal panel or on a flexible wiring substrate.
As shown in FIG. 8A, when mounting an IC using such an anisotropic conductive film 6, the film is deposited on an IC mounting region 9 of a substrate, such as a glass or flexible wiring substrate. A driving IC 13xe2x80x2 is then arranged on the surface of this anisotropic conductive film 6. Next, as shown in FIG. 8B, the driving IC 13xe2x80x2 is mounted to the substrate by thermal compression bonding using a bonding head 5. As a result, the resin component of the anisotropic conductive film 6 is melted and fluidized. Thereafter, the anisotropic conductive film 6 is cured, and then the resin component of the anisotropic conductive film 6 is solidified, to mount the driving IC 13xe2x80x2 onto the IC mounting region 9. During this step, the bump electrodes 130xe2x80x2 of the driving IC 13xe2x80x2 are electrically connected to electrode terminals 16 on the substrate side through conductive particles 60 contained in the anisotropic conductive film 6. Here, the number of conductive particles 60 positioned between the bump electrodes 130xe2x80x2 and the electrode terminals 16 greatly influences the electrical resistance, reliability, etc.
In this mounting structure, each bump electrode 130xe2x80x2 of the driving IC 13xe2x80x2 is conventionally formed at a pitch of approximately 100 xcexcm, and the shape of the bump electrodes 130xe2x80x2 is straight with a fixed width. The surface of the bump electrodes 130xe2x80x2 facing, i.e., opposing, the electrode terminals 16 may be curved.
However, in a liquid crystal device (e.g., a liquid crystal display device), the bump electrodes 130xe2x80x2 tend to be arranged in higher density as the number of pixels increases, which causes a problem that makes it difficult, if not impossible, to even use conventional bump electrodes 130xe2x80x2 in liquid crystal devices. That is, when the bump electrode density is increased such that the pitch of the bump electrodes 130xe2x80x2 is approximately 40 xcexcm, conductive particles 60 will gather in high density between adjacent bump electrodes 130xe2x80x2 when the anisotropic conductive film 6 is melted, causing short-circuiting between bump electrodes 130xe2x80x2. On the other hand, when the bump electrodes 130xe2x80x2 are made narrower in width, the number of conductive particles 60 between the bump electrodes 130xe2x80x2 and the electrode terminals 16 will decrease, impairing the electrical characteristics (e.g., resistivity, etc.) and reliability of the device.
Therefore, it is an object of the present invention to overcome the aforementioned problems.
It is another object of the invention to provide an IC and a mounting structure thereof with an improved bump electrode structure, whereby the bump electrodes are electrically connected to electrode terminals on a substrate through an anisotropic conductive film without compromising, or causing deterioration of, the electrical characteristics or reliability, even when the bump electrodes are formed with a narrow (e.g., small) pitch.
It is further object of the invention to provide a liquid crystal device employing such an IC or mounting structure thereof
It is yet another object of the invention to provide an electronic apparatus employing such an IC or mounting structure thereof.
To achieve the above objects, one aspect of the invention provides a semiconductor device comprising a first substrate, and a plurality of electrodes, each having a base portion formed on the first substrate and an upper portion, and each adapted to be electrically connected to a corresponding electrode terminal on a second substrate through an anisotropic conductive film containing conductive particles. In accordance with the invention, the base portion of each electrode has a cross-sectional width that is substantially less than the cross-sectional width of the upper portion facing the corresponding electrode terminal to the base portion.
When the semiconductor device of the present invention is mounted to a substrate through an anisotropic conductive film to electrically connect the electrode terminals on the second substrate and the bump electrodes on the semiconductor device side, the resin component of the anisotropic conductive film is melted and the conductive particles will flow from the inner areas between the semiconductor device and the substrate toward the outer periphery. Because the base portions of the bump electrodes are made narrower, there are wide gaps between the base portions of adjacent bump electrodes even when such electrodes are formed in high density. Thus, when the anisotropic conductive film is melted and the conductive particles flow from the inner area between the semiconductor device and the substrate toward the outer periphery of semiconductor device, a large number of conductive particles do not gather between adjacent bump electrodes, so that the conductive particles do not cause short-circuiting between the bump electrodes. Further, although the bump electrodes are made narrower at the base portion, the upper portions thereof facing the electrode terminals of the substrate are wider, such that the area of the surface of each bump electrodes which faces a corresponding electrode terminal is large. Thus, a large number of conductive particles exist between the bump electrodes and the electrode terminals, so that a satisfactory electrical connection is effected between the bump electrodes and the electrode terminals. Thus, even if the bump electrodes of the semiconductor device are formed in high density, it is possible to achieve a high level of reliability.
The semiconductor and semiconductor mounting structure of the present invention is applicable to various types of semiconductor devices. In a liquid crystal device, the semiconductor device of the present invention is effectively mounted on either one of the substrates forming a liquid crystal panel or on a wiring substrate electrically connected to the liquid crystal panel. When such a liquid crystal device is used as a display device for an electronic apparatus, such as a mobile telephone, a higher display quality can be achieved without compromising reliablity. By utilizing a semiconductor device of the present invention, which permits a higher density arrangement of bump electrodes without short circuiting the device, the number of display pixels in the liquid crystal device can be increased to increase display quality. Although a large number of conductive particles do not gather between bump electrodes to create short circuiting problems, a large number of such particles are secured between the bump electrodes and the electrode terminals, thereby making it possible to effect satisfactory electrical connection between the bump electrodes and the electrode terminals.
The invention also provides a method of manufacturing a semiconductor device. The method comprises forming a plurality of electrodes on a surface of a semiconductor substrate, applying a photosensitive resist layer to the surface of the semiconductor, exposing the photosensitive resist layer to light through an exposure mask having a plurality of shielding portions, each aligned with a respective one of the plurality of electrodes, creating a plurality of openings in the photosensitive resist layer, each opening being aligned with a corresponding one of the plurality of electrodes and having a reversed-taper shape, filling the plurality of openings with an electrode plating material; and removing the photosensitive resist layer.